CD137 is a member of the tumor necrosis factor (TNF) receptor family. Its alternative names are tumor necrosis factor receptor superfamily member 9 (TNFRSF9), 4-1BB and induced by lymphocyte activation (ILA). CD137 can be expressed by activated T cells, but to a larger extent on CD8 than on CD4 T cells. In addition, CD137 expression is found on dendritic cells, follicular dendritic cells, natural killer cells, granulocytes and cells of blood vessel walls at sites of inflammation. One characterized activity of CD137 is its costimulatory activity for activated T cells. Crosslinking of CD137 enhances T cell proliferation, IL-2 secretion survival and cytolytic activity. Further, it can enhance immune activity to eliminate tumors in mice.
CD137 is a T-cell costimulatory receptor induced on TCR activation (Nam et al., Curr. Cancer Drug Targets, 5:357-363 (2005); Watts et al., Annu. Rev. Immunol., 23:23-68 (2005)). In addition to its expression on activated CD4+ and CD8+ T cells, CD137 is also expressed on CD4+CD25+ regulatory T cells, natural killer (NK) and NK-T cells, monocytes, neutrophils, and dendritic cells. Its natural ligand, CD137L, has been described on antigen-presenting cells including B cells, monocyte/macrophages, and dendritic cells (Watts et al., Annu. Rev. Immunol., 23:23-68 (2005)). On interaction with its ligand, CD137 leads to increased TCR-induced T-cell proliferation, cytokine production, functional maturation, and prolonged CD8+ T-cell survival (Nam et al., Curr. Cancer Drug Targets, 5:357-363 (2005), Watts et al., Annu. Rev. Immunol., 23:23-68 (2005)).
Signaling through CD137 by either CD137L or agonistic monoclonal antibodies (mAbs) against CD137 leads to increased TCR-induced T cell proliferation, cytokine production and functional maturation, and prolonged CD8+ T cell survival. These effects result from: (1) the activation of the NF-κB, c-Jun NH2-terminal kinase/stress-activated protein kinase (JNK/SAPK), and p38 mitogen-activated protein kinase (MAPK) signaling pathways, and (2) the control of anti-apoptotic and cell cycle-related gene expression. Experiments performed in both CD137 and CD137L-deficient mice have additionally demonstrated the importance of CD137 costimulation in the generation of a fully competent T cell response.
IL-2 and IL-15 activated NK cells express CD137, and ligation of CD137 by agonistic mAbs stimulates NK cell proliferation and IFN-γ secretion, but not their cytolytic activity. Furthermore, CD137-stimulated NK cells promote the expansion of activated T cells in vitro. In accordance with their costimulatory function, agonist mAbs against CD137 have been shown to promote rejection of cardiac and skin allografts, eradicate established tumors, broaden primary antiviral CD8+ T cell responses, and increase T cell cytolytic potential. These studies support the view that CD137 signaling promotes T cell function which may enhance immunity against tumors and infection.
Other anti-CD137 antibodies have been disclosed in U.S. 2005/0095244, issued U.S. Pat. No. 7,288,638 (such as 20H4.9-IgG4 [10C7 or BMS-663513] or 20H4.9-IgG1 [BMS-663031]); U.S. Pat. No. 6,887,673 [4E9 or BMS-554271]; U.S. Pat Nos. 7,214,493; 6,303,121; 6,569,997; 6,905,685; 6,355,476; 6,362,325 [1D8  or BMS-469492; 3H3 or BMS-469497; or 3E1]; U.S. Pat. No. 6,974,863 (such as 53A2); or U.S. Pat. No. 6,210,669 (such as 1D8, 3B8, or 3E1). Additional CD137 agonistic antibodies are described in U.S. Pat. Nos. 5,928,893; 6,303,121 and 6,569,997.
These and other deficiencies in the previous antibodies are overcome by the provision of fully human antibodies to CD137 by the present disclosure.